(a) Field of the Invention
The present invention relates to an objective lens system for microscopes, and more specifically to an objective lens system for incident light fluorescence microscopes.
(b) Description of the Prior Art
Conventionally, there have been no objective lens systems designed especially for fluorescence microscopes, and ordinary type of objective lens systems having relatively high transmittance for excitation light (mainly ultraviolet rays) were selected for fluorescence microscopy. However, ordinary type objective lens systems designed for mgnification levels on the order of 10.times. have numerical aperture (NA) of 0.2 to 0.25 and, even when they show relatively high transmittance for excitation light, it is not high enough for fluorescence microscopy. In such objective lens systems, excitation light is attenuated rather remarkably before reaching a specimen as compared with intensity of incident light. Further, since fluorescence emitted from a specimen is very weak, objective lens systems having small NA remarkably darken images observed through fluorescence microscopes. In order to eliminate these defects, it is required to design an objective lens system which shows high transmittance for excitation light and has a large NA. Moreover, an objective lens system having a large NA is preferable for enhancing resolution even for purposes other than fluorescence microscopy.